The present invention relates to a dual mass vehicle driveline master clutch. More specifically, the present invention relates to a dual mass vehicle driveline master clutch where the rotating inertia of the clutch when disengaged is minimized to reduce torsional vibration levels at low engine speeds.
The present invention relates to an apparatus for damping the torsional vibrations generated by a firing internal combustion engine which are transferred into the driveline via the master clutch. It is known to use split dual flywheels, one on each side of a compliant member such as a spring damper to lower the level of these torsional vibrations where a clutch assembly is attached to the second flywheel and contributes to its rotational inertia. It is also known to use dual masses without a split flywheel with one rotational inertial mass upstream of the damper and a second rotational inertial mass downstream of the damper to lower the level of torsional vibrations transferred to the driveline. Both of these systems can improve overall vehicle driveability and increase the service life of the various driveline components.
U.S. Pat. Nos. 5,374,218; 5,273,372 and 5,788,037, the disclosures of which are hereby expressly incorporated by reference, all disclose various variations of dual mass and split flywheel type systems for lowering torsional vibrations. U.S. Pat. No. 5,788,037 discloses a clutch system where the rotational inertia of the clutch input hub is increased with the addition of weights in an effort to more effectively control torsional vibration generated by the engine at the engine firing frequency. This prior art system has one significant disadvantage in that the torsional vibrations during engine start-up will be increased by the added mass to the clutch.
In a dual mass split flywheel system, the mass of the flywheel is split into a first mass and a second mass where the first mass is attached to the engine side of the damper and the second mass is attached to the clutch side of the damper.
It would be advantageous if the torsional natural frequency of the flywheel/clutch system could be raised during engine start-up and then lowered for more effective control of the driveline torsional vibration levels due to engine firing in normal operation.
More specifically, the major problem with the prior art dual mass and split flywheel and other dual mass systems is that the natural frequency of the system is relatively low even when the master clutch is disengaged. This creates a problem when the engine is started in that the frequency of the torsional vibration excitation generated by the engine at some point in the engine start-up sequence matches the natural frequency of the prior art dual mass system causing high vibration levels in the driveline and into the passenger compartment.
In general, the first rotational mass of a dual mass system consists of the engine flywheel and the second mass consists of a clutch input assembly which includes the input shaft, the clutch input hub and the drive friction discs when the clutch is disengaged and in addition, the clutch driven friction discs and output hub when the clutch is engaged. The first mass is connected to the second mass through a damper element which is commonly a spring damper which contributes to both inertia masses. The rotational inertia and hence the torsional natural frequency of the dual mass system varies according to the state of engagement of the clutch assembly. In general, as the excitation frequency produced by the engine matches the natural frequency of the flywheel/damper/clutch system, the resulting torsional vibration levels increase dramatically until the engine reaches a sufficient speed so as to increase the engine""s excitation torsional frequency above the natural frequency of the flywheel/damper/clutch system. High levels of driveline torsional vibration can damage the driveline and are disconcerting to the operator.
The present invention provides for a reduced level of torsional vibration produced in the driveline and then transferred into the vehicle cab at very low engine speeds and especially during engine start-up. Engine start-up is commonly performed with the clutch disengaged and to perform as intended, the present invention requires this. According to the present invention, the rotational moment of inertia of the second mass (limited to the rotating portion of the clutch assembly when the clutch is disengaged) is minimized by designing the clutch input assembly to minimize its rotational moment of inertia thereby lowering the torsional resonant frequency of the dual mass system when the clutch is disengaged. After the engine reaches a minimum speed, the clutch can then be engaged to link the engine to the complete clutch assembly thereby lowering the torsional natural frequency of the dual mass system for more effectively reducing torsional vibration at higher engine speeds.
Thus, according to the present invention, the difference in magnitude between the rotational inertia of the clutch when engaged verses the rotational inertia when disengaged is significantly increased as compared to prior art systems in order to raise the torsional natural frequency of the dual mass system above the engine firing frequency during engine start-up with the clutch disengaged. The rotational moment of inertia of the clutch input assembly which rotates with the engine irrespective of the state of the clutch, is lowered by decreasing its diameter so that it fits inside the envelope of the clutch output hub. The clutch drive friction discs are also downsized and driven on their inside diameter. After engine start, the clutch is engaged and the torsional resonant frequency of the dual mass system is then lowered to more effectively reduce torsional vibration.
One provision of the present invention is to minimize the rotating moment of inertia of the clutch assembly when it is disengaged as compared to its rotating moment of inertia when the clutch assembly is engaged.
Another provision of the present invention is to minimize the rotational moment of inertia of the clutch assembly when it is disengaged as compared to its rotational moment of inertia when the clutch assembly is engaged by minimizing the rotational moment of inertia of a clutch input assembly.
Still another provision of the present invention is to reduce the magnitude of driveline torsional vibrations during engine start-up by disengaging the clutch and minimizing the rotational inertia of the clutch input assembly to raise the torsional natural frequency of the rotating driveline.